1. Field of the Invention
The present invention relates to a method for forming an image using an electrophotographic technology.
2. Description of the Related Art
In recent years, the spread of a copying machine and a printer using electrophotography requires further improvements thereof in terms of speed-up, downsizing, full-colorization, and a high image quality. In addition, as the user thereof expands, the lower priced copying machines and printers and improved maintenance-free abilities thereof have also been demanded. Therefore, as regards the main body of each of those machines, the number of structural components should be decreased and also the machine configuration should be simplified.
Consequently, technical requirements for consumable supplies such as a toner and a drum have increased in year after year. In addition, as a developing method, attention is directed toward a contact developing method using a nonmagnetic one-component developer.
A toner particle in a nonmagnetic one-component developer is more excellent in fixing ability at low temperature than a magnetic toner. In addition, such a developer does not contain an opaque magnetic material, so that the developer is suitable for obtaining a color image such as a full- or multiple-color image and can be used with a light-transmitting medium such as an overhead transparency film (i.e., an OHP film). Furthermore, one of the features of such a consumable developer is its simple structure, so that the machine can be downsized and maintenance-free.
As stated above, the nonmagnetic one-component developing method is a very suitable for attaining various kinds of requirements such as downsizing the machine, making the machine maintenance-free, making an image of much finer resolution, and providing a full-color image.
For meeting the requirement of downsizing the image forming apparatus using an electrophotographic system, such as a copying machine, a printer, or a facsimile machine, there is a tendency of reducing diameters of a toner bearing member and a toner-supplying member for supplying a toner to the toner bearing member. Furthermore, there is an additional requirement for speeding up, so that an extremely high process speed is required when trying to obtain the downsized and high-speed machine. Thus, the toner bearing member and the toner-supplying member need to rotate at high speed. At this time, a rub between the toner-supplying member and the toner bearing member and a rub between the toner bearing member and a toner regulating member accelerate toner deterioration. Consequently, the toner deterioration leads to a decrease in developing ability of the toner, resulting in poor quality ability of an image to be formed.
On the other hand, there is proposed a technology for increasing the durability of electric charges retained on the toner and environmental stability thereof by specifying the electric resistivity of the nonmagnetic one-component developer (see JP 07-43546 B). In addition, there is also proposed a technology to suppress a decrease in quality of an image by controlling the degree of aggregation of a toner in the nonmagnetic one-component development (see Japanese Patent No. 3272056).
Furthermore, for suppressing the deterioration of a toner-supplying roller, there is proposed a technology to make the diameter of the toner-supplying roller larger than that of a developing roller (see JP 05-257376 A). In addition, JP 06-289705 A discloses a device in which the diameter of a toner-supplying roller is designed to be larger than the diameter of a developing roller.
However, further improvements have been needed for the method for forming an image capable of effectively suppressing the toner deterioration due to rubbing and also capable of keeping the high quality image.